Aircraft landing gear



R. A. FELBURG 2,399,218

Filed sept. 7, 194s s sheets-sheet -1 ff Q E im e "minimii April 3o, 1946.

AIRCRAFT LANDING GEAR April 30, 1946e R. A. FELBURG AIRCRAFT LANDING GEAR Filed Sept. 7, 1945- 3 Sheets-Sheet .2

R. A. FELBURG AIRCRAFT LANDING GEAR `Filed sept. '7, 1943 April 3o, 1946.

3 Sheets-Sheet 3 mm. .m

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mf M -INVENTOR. 552e C` Arf-0f? /vf Patented Apr. 30, 1946 UNITED STATES PATENT OFFICE AIRCRAFT LANDING GEAR Robert A. Felburg, Newark, N. J. Application September 7, 1943, Serial No. 501,472 (Cl. 244-103) 12 Claims.

My invention relates broadly to aircraft operation and more particularly to the conditioning of aircraft landing gear for effecting landing operations.

One of the objects ofA my invention is to provide a system for increasing the life of aircraft landing gear by reducing the frictional wear on the treads of the tires of the aircraft landing gear by initiating the landing Wheels to a speed of rotation in preparation for landing at substantially the approximate speed that the ltires will contact the runways at the instant of landing.

Another object of my invention is to provide means for conditioning the wheels of aircraft landing gear for reducing wear on the treads of such wheels Without necessitating reconstruction of standard aircraft landing gears in any way.

Still another object of my invention is to provide means applicable for installation upon aircraft for imparting rotative motion to the landing Wheels of aircraft preliminary to landing which means may be' coordinated with standard retractible aircraft landing gear Without modification of the construction of the retractible landing gear.

A further object of my invention is to provide means for impartingrotative motion to the wheels of aircraft landing gear preliminary to a landing operation in which the means are rendered automatically ineffective when the landing wheels have been brought up to proper landing speed.

A still further object of my invention is to prol vide a construction of automatic indicator means for visually indicating to the pilot when either or both of the landing wheels on the aircraft have been brought up to proper landing speed preparatory for effecting a landing operation.

Another object of my invention is to provide a novel construction of centrifugally operated speed governing means for automatically rendering the driving means for the landing wheels of aircraft ineffective when a, proper landing speed has been reached.

Other and further objects of my invention reside in the construction and arrangement of driving means for association with standard retractible aircraft landing gear for imparting rotative movement to the wheels of the standard landing gear preparatory to a landing operation as set forth more fully in the specification hereinafter following by reference to the accompanying drawings, in which:

Figure 1 schematically illustrates the application of the system of my invention to conventional aircraft landing gear, the view-,illustrating the normal condition while the aircraft is in flight and prior to application of the drive means to the treads of the aircraft landing wheels; Fig. 2 is a schematic view of the arrangement illustrated in Fig. 1 but showing the position of the drive means when the pilot closes the control switches preparatory for a landing operation and for imparting rotative movement to the treads of the landing wheels; Fig. 3 is a further schematic view showing a modified arrangement of the drive means for imparting rotative movement to the wheels of the retractible aircraft landing gear by engagement of the drive means with the sides of the casings of the tires in retracted' position as distinguished from engagement -with the treads of the tires in the arrangement illustrated in Figs. 1 and 2; Fig. 4 is a schematic view of the arrangement shown in Fig. 3 where the pilot has operated the circuit closing means displacing the driving means to a position engaging the sides of the tire casings for imparting rotative movement thereto prior to effecting a landing operation; Fig. 5 is a diagrammatic view illustrating the control means for each wheel of the retractible landing gear in position prior to the closing of the control circuit before preparing for a landing operation; Fig. 6 is a fragmentary view showing the association of the control means with the control board of the aircraft and illustrating the manner in which the circuit closing means for each aircraft landing gear also serves as an indicator for informing thepilot when the wheels reacha proper rogoverning mechanism associated therewith with parts broken away and illustrated in section withr the parts in operative position for closing the electrical circuit therethrough for all normal speeds below a predetermined excess speedy; Fig. 8 illustrates the parts of the mechanism of Fig. 7 displaced under conditions of excessive speed for opening the circuit through the governor mechanism; Fig. 9 is a transverse sectional view taken substantially on line 9-9 of Fig. '7; Fig. 10 is a front elevational view of the pilot control switches and indicator mechanism which serves |both as a control means for initiating the driving mechanism in operation preparatory for landing and also as a visual indicator to inform the pilotwhen each landing wheel is brought up to proper speed; Fig. 11 is a longitudinal sectional view taken on line ll-Il of Fig. 10 and showing the magnetic shield which is employed arrangement for preventing adverse influence of the switch mechanismA upon the instruments on the instrument board of the aircraft; and Fig. 12 is a transverse sectional view taken on line l2| 2 of Fig. 11.

My invention is directed to an aircraft retractible landing gear of a construction designed to save and conserve the rubber tires of the aircraft landing gear. I provide mechanism winch may be installed on aircraft of 'any standard type without change to the 'retractible landing gear. The mechanism of my invention is wholly independent of the character of constructionof the retractible landing gear and is therefore generally applicable to all types of retractible landing gears. It is realized that production and manufacture of retractible landing gears involves a highly complicated and detailed problem and any change in the landing gear structure per se to produce rotation of the landing wheels is impracticable because of the necessity of freezing designs and constructions under existing manufacturing conditions. I therefore adapt the mechanism of my invention to any design of retractible landing gear without change in the landing gear construction. I provide friction drive wheels located adjacent the landing gear wheels when moved to retracted positions with means for effecting engagement between the friction drive wheels and the landing wheels of the aircraft landing gear for imparting rotation to the landing wheels for bringing the landing wheels up to speed so that the wheels are rotating at approximately landing speed when the aircraft initially contacts the ground. The friction drive mechanism is operated under control of the .pilot at a reasonable time prior to landing. The control mechanism is so arranged that the mechanism also serves as an indicator to the pilot when the landing wheels have been brought up to required speed so that the friction drive mechanism is withdrawn from engagement with the landing wheels at the proper time and the pilot thus infomed of the fact that both landing wheels are spinning at the proper speed for efiecting a safe landing.

As an example of the application of my invention, certain types of bombers cannot land at an air speed of less than 120 miles per hour so that in order to effect a safe landing, the bomber is normally piloted from an air speed of say something above 160 miles per hour in an eort to bring the bomber down to a safe landing speed. The pilot may attempt to come in at an air speed of approximately 140 miles per hour. Approximately ten minutes before landing, the pilot may be informed from the landing field of a 30 mile per hour wind over the eld. As the pilot must land into the wind, he mentally subtracts 30 ,from

140 and knows that his landing speed should be approximately 110 miles per hour. He `then closes the circuits to the friction drive means of my invention, operating to bring up the landing wheels to speed safe for landing. The friction drive means are automatically controlled so that should the landing wheels exceed the required landing speed, the driving force is removed and the wheels allowed to spin preparatory to landing, the pilot being informed of the rotating condition by indicator means on the control board in the pilots position.

The friction drive mechanism comprises a small electric motor installed within each wing adjacent the position in which the landing gear i around the' control switch and holding magnet is retracted. The small electric motor located adjacent each wheel operates a friction drive wheel which may be moved into engagement with the tire of the landing wheel either with respect to the tread or the side of the casing for bringing the landing wheel up to speed. The movement of the positiony oi the motor is effected by magnetic control 'meansenergized under control of the pilot from a control position on the pilots control panel. The motor carriesa centrifugally operated switch that is designed to open the circuit to the driving motor when the driving speed reaches a safe landing speed whereupon the control means, which also serves as a visual indicator,

moves to a release position thereby informing` the pilot with respect to the sate rotating speed of the landing wheels. A separate friction drive system is provided for each landing wheel because of differences in friction and other conditions which may result in one landing wheel reaching landing speed prior to the other landing wheel. The landing wheels may attain a speed above landing speed in just a few minutes of application of the friction driving means to the landing wheels. The friction drive means are then moved out of engagement with the landing wheels and the driving motors cut off. Then, approximately ve minutes before landing, the landing wheels are lowered out of the wings into extended position for landing and by the time the plane is ready to contact the ground, the landing wheels will have slowed to approximately landing speed. For example, if the landing wheels have been driven to attain a speed of 200 miles per hour, the wheels may be rotating at 160 miles per hour at the time the plane is ready to land. lf the plane lands at miles per hour, then even though the wheels may be rotating at either 10 or 15 miles per hour slower or faster, very little rubber is worn from the landing wheels in view of the relatively small friction wear which occurs in the instant of contact between the tires and the rimway.

Referring to the drawings in more detail, reference character I schematically represents the chassis of the aircraft having wing structures 2 and 3 projecting therefrom. The conventional retractible and extendable landing gear is represented in Fig. 1 in full lines at 4 and 5 in retracted position and is shown in extended positions in dotted lines at 4 and 5'.

The retractible and extendable -landing gear l is of conventional form and has been shown as including a strut 8 of the telescopic Oleo type having two telescopically associated relatively slidable portions 1 and 8 and interconnecting links 9 and I0. The strut terminates in a yoke Il which `iournals the wheel represented at l2. The same parts have been designated by primed characters 1', 8', 9', Ill', Il', and i2' in the extended position of the landing gear shown in dotted lines. The retraotible landing gear 5 includes corresponding parts constituted by strut I4 of the telescopic Oleo type having two telescopically associated relatively slidable portions i1 and il controlled by links I9 and 20 and supporting yoke 2| in which landing wheel 22 is journalled. The dotted line position of the retractible landing gear shows the corresponding parts indicated by primed characters at l1', i8', I9', 2li', 2| and v 22'. The retractible and extendable landing gear 4 is pivoted about axis 23 Yand is movable into and out of the wing structure 2 through opening 2l beneath the wing structure 2. The retractible and extendable landing gear 5 is pivoted at 2l movement sufficient to eilect frictional driving engagement between friction wheel 3o driven by shaft 2l of the electric motor system and the landing wheel of the retractible and extendable landing gear. In Figs. 1 and.2, I show the two f extreme positions of the electric motor drive mechanism, Fig. 1 illustrating the electric motor drive mechanisms in normal rest condition with friction drive wheel 30 disengaged 'by landing wheel i2KV while Fig. 2 shows friction drive wheel 30 engaged with landing wheel l2. This restricted angular movement is allowed by reason of the mounting of the electric motor mechanism as shown more clearly in Fig. where the the normal position for electric motor mechanism 21 is shown. An actuating rod 32 extends from the frame of the electric motor mechanism 21 and provides a connection at its extremity shown at 33 for spring 3d which is fixed relatively Yto the wing structure as represented at 35. A stop @d provides an abutment for rod member 32 whereby the electric4 motor mechanism 21 is normally maintained in a position in which friction wheel 3@ is disengaged from landing wheel i2. Rod member 32 yalso provides a connection at t1 through link 38 with an armature member t9 of solenoid 2li; Solenoid im has an electromagnetic winding thereon which is electrically connected at one end to the terminal di of the control switch and indicator represented at t2. The control switch and indicator d2 includes a single throw knife bladel member et pivoted with respect to terminal di and normally spring pressed to open position by spring member it seated in l socket t5 in the insulated base t8 of the control switch and indicator. The insulated base i6 carries a jaw-type contact d1 into which the switch blade llt is adapted to be pressed against the action of spring M. The-switch blade t3 carries an armature member d3 thereon which is adapted to be aligned with the electromagnet represented at t9 which operates as a holding magnet. Electromagnet d@ is electrically connected in series with source of potential represented at 5G from which a circuit is completed through conductor 5l to the windings of electric motor mechanism 21 and thence through conductor 52 to the centrifugally operated switch contact mechanism arranged within housing '53, shown more clearly in Figs. 7-9, of the electric motor mechanism 21. The circuit continues from the centrifugally opferated switch mechanism in housing 53 through conductor 5t to the solenoid winding d.

mains .energized so long as the driving motor mechanism is being brought up to speed and is maintained at a speed below excessive speed as determined by the governing mechanism explained in Figs. 7-9. It will be seen that the energization of solenoid 40 brought about by closing circuit'I from source 50 through switch blade 43 and contact 41 serves to angularly shift the frame 21 of the motor mechanism about pivot 29 for moving friction drive wheel -30 into engagement with landing wheel i2. When the landing wheel i 2 exceeds the desired landing speed the governing mechanism within housing 53 opens the circuit through solenoid t0 allowing the frame of the electric motor mechanism-to swing to the position shown in Fig. 5 disengaging friction drive wheel 30 from landing wheel l2 and opening the circuit to the driving motor windings through switch blade d3 and contact t1 and opening the circuit through holding magnet t9. Switch Ablade 213 is thus pushed open by spring t4, knob lit projecting forward on the pilots control board and indicating to the pilot that the landing wheel i2 has been brought up to a safe landing speed. C

The landing wheel 22 is provided with an arrangement of electric motor drive mechanism similar to the drive explained for landing wheel i2. The reason for the independent control circuit for the drive mechanism for landing wheel 22 is to provide means for bringing up the two landing wheels to proper speed independently of variations in friction or differences in journalling arrangements. The parts for the two independent controls are similar and I have accordingly indicated the several parts by corresponding reference characters with subscripts a applied thereto as shown. It will be understood however that the power source ta is the same power source as that indicated at 5@ and that two independent power sources are not necessary. Moreover the control switches and indicators 63 and @3a of each are mounted in the same magnetically shielded casing 51 and I have accordingly indicated the magnetic shield 51 by the same reference character in each portion of the Vview illustrated in Fig. 5. The control members and indicators 5t and 56a each project from the magnetically shielded housing on the pilots control panel 85 It will be observed that the switch blade d3 terminates in an operating handle 55 Iwith a knob Stroh the end thereof extending outside the casing 51 of the control switch and indicator through aperture 5B. The casing 51 constitutes a magnetic' shield including a shielding partition v51a for preventing any magnetic influence from holding magnet t9 from aecting the meters and indicators 59, 6U, 6l, 62, 63, t4. etc. associated on the pilots control board shown schematically in Fig. 6. The control switch and indicator remains in closed position so long as holding as shown in Fig. 6 so that th'e pilot will be informed when one landing wheel l2 is brought up to proper landing speed and will also be informed when the other landing wheel 22 is brought up to proper landing speed by the positions of the control members and indicators 5t and 56a. In each instance, as the circuit is opened between the switch plates d3 and contact i1 and switch plate 'tta and contact 41a, the electric motor driving mechanism 21 and 28 is angularly shifted about pivots 29 and 29a, thus removing friction drive wheels 3E and 30a. from engagement with landing wheels i2 and 22.

The disengaging position for the friction driving wheels 30 and 30a with respect to landing wheels I2 and 22 is illustrated in Fig. 1 whereas the engaged position between friction driving wheels 30 and 30a with the threads of tires on landing wheels i2 and 22, respectively, is illustrated in Fig. 2.

In Figs. 3 and 4.1 have illustrated the electricv motor drive mechanism in the wing structures of the aircraft for frictionally driving the landing wheels I2 and 22 by engagement with the side walls of the tire casings i2 and 22`instead of with -magnet t9 is energized. Holding magnet 49 re- '.575 the treads of the tires. Fig. 3 shows the frictional driving wheels 30 and 30a in normal position disengaged from the walls of the tire casing of the landing wheels I2 and 22, whereas Fig. 4 shows the electric motor driving mechanisms 21 and 23 disengaged by the closing of the electric control circuits to eect engagement between friction driving wheels 30 and 30a with the side walls of the casings of the tires |2 and 22. As the landing wheels are brought up to proper landing speed, the electric motor driving mechanisms are restored to the positions illustrated in F18. 3 by the action of springs 34 and 34a. The solenoids 40 and 40a are deenergized by opening of the series control circuit between switch plate 43 and contact 41 and switch plate 43a and contact 41a upon deenergizatlon of holding magnets 43 and 43a due to an overspeed condition at the cen trifugal switch control mechanism illustrated in Figs. 7-9.

Referring to Figs. 7-9, the motor shaft 3|, which extends from the electric motor 21, carries the friction drive wheel 30 for engagement with the landing wheels I2 or 22.l The shaft extends through a housing 53 having an anti-friction bearing connection with shaft 3| as represented at 36. The housing 53 thus serves as a dust and moisture-tight cover for the precision mechanism contained therein.

The speed governing mechanism includes a sleeve member 61, secured by set screw 33 to a selected position on shaft 3|. The position of sleeve 61 may be adjusted longitudinally of the shaft for increasing or decreasing the speed at which the governor mechanism operates to open the series circuit to the driving motor mechanism. Sleeve 31 is provided with pairs of radially projecting lugs represented at 33 and 10, forming pivot means for arms 1| and 12 which carry centrifugally operated weights 13 and 14 on the ends thereof. Arms II and 12 have lugs 15 and 13 extending inwardly therefrom forming pivotal connections for link members 11 and 13 which pivotally connect with radially extending lugs 13 and 80, carried by longitudinally slidable sleeve member 8|. The longitudinally slidable sleeve member 3| has an inwardly projecting key 32 thereon, which is longitudinally slidable in a keyway or slot 33 formed in shaft 3|. As the weights 13 and 14 swing outwardly under centrifugal force due to increased speed of shaft 3| and friction drive wheel 30 in frictional engagement with landing wheel I2 or 22, a pull is exerted on'sleeve 3| displacing sleeve'3I longitudinally of shaft 3|.

Sleeve 3| cannot turn relatively to shaft 3l but' is only slidable longitudinally with respect thereto. The sleeve 8| has a radially extending flange 84 on the end thereof opposite to the end at which links 11 and 13 pivotally connect. The faces of flange 34 provide slidable connection with collar member 85 through the ball races indicated at 33 and 31 secured in ball race plates 33 and 33. The collar member 85 ha's a pair of longitudinally extending arms 3 0 and 3| with hookshaped ends 30o and 3Ia for engagement with the inwardly extending flange 32 of collar member 33. Collar member 33 has an annular space therein indicated at 34, within which the hook-shaped ends 30a and 3Ia of members 30 and 3| are free to be displaced longitudinally within definite limits. Thus a lost motion connection is provided between collar member 33 and the system of centrifugal weights including weights 13 and 14.

Sleeve member 34 projects from the housing of the motor 21 and terminates shortLv beyond :,soasns nism and serves as a support and guide for the parts .to which the collar assembly 33 is connected. The extremity of the sleeve 34 is grooved at 30h and 3Ib to allow the longitudinal movement of the arms 30 and 3| under centrifugal action of the switch control mechanism. 4.Anti-friction bear ings 35 and 33 are provided between shaft 3| and sleeve member 34 for maintaining accurate align'- ment of the parts and reducing friction to a minimum.

The collar assembly 33 has an insulated bushing 31 and a ring member 33 secured thereto by screw members 33. Insulated bushing 31 slidably connects with sleeve member 34 and may be displaced longitudinally thereof. The insulated bushing 31 serves as an insulated support for the annular conductive ring member |00. The securing screws 33 are countersunk in insulated bushing 31 and thus do not electrically connect with ring member |00. The ring member |00 is provided with an inwardly extending flange I00a fitting within an annular groove in insulated bushing 31 for forming a. substantial mechanical connection therewith while at the same time maintaining ring member |00 in substantial insulated relation to all parts of the collar assembly 33. There is embedded in insulated bushing 31 an eyelet member |0I in insulated relation to ring member |00, ring member 33 and the other parts of the collar assembly 33. The eyelet IOI provides a connection for coil spring |02 which is secured at the other end |03 to theframe of the motor 21. Coil spring |02 tends to continuously draw the collar assembly 33 toward the motor frame 21 for maintaining the face of conductive annular ring |00 in electrical connection with the contact segments |04 and |05 forming the terminals for the series circuit through conductors 52 and 54 in the series control path explained in Fig. 5. The segments |04 and |05 are insulatingly mounted as represented at |08 and |01 in the extremity of the tubular frame member |03 that projects from the motor frame 21. The conductors 52 and 54 enter opposed sides of housing 53 through insulated bushings |03 and IIO as shown and electrically connect with segments |05 and |04. 4-

Under normal conditions of rotati'omcoil spring |32 maintains the annular conductive'ring |00 in contact with the segments |04 andl |05. However as the speed increases, the centrifugal weights move outwardly, displacing sleeve 3| longitudinally of the `shaft system until a position is reached in which the hook-shaped ends 30a and 3|a of arms 30 and 3| pull the collar assembly 33 further away from the end of tubular member |33, as represented in Fig. 8, separating the annular conductive ring member |00 from electric circuit connection with segments |04- and |05, thus opening the series circuit path illustrated in Fig. 5 which results in the deenergizationof holding magnet 43. Spring 44 then forces plate 43- to be disengaged from electric circuit connection with contact 41, thereby opening the series circuit path to solenoid 40 and to the driving motor 21. The motor thus shuts down and coilspring 44 angularly shifts the motor out of position so that 'friction drive wheel 30 is disengaged from the landing wheel I2. This same series'of steps 4occurs with respect to landing wheel 22 'audits associated control mechanism. The pilot is at once informed, despite the fact that the landing wheels are belowvthe aircraft and out of the range of the pilots vision, of this existing condition by the inthe closed circuit position for governing mechadicators 53 and 53a which are visually displaced on the pilots control panel 65' as represented in Fig. 6.

For purposes of explaining the principles of my invention, I have shown only one method of `folding the landing gear into the wings of the aircraft. However, it will be understood that my invention is equally applicable to the various systems employed in retractible landing gear where the wheels may fold inwards; outwards, backwards with a half twist, into Wells in the wings or straight' back into space in the engine nacelles. It will' accordingly be understood that my invention is equally applicable to any of the various constructions of retractible landing gears.

I have shown individual motors for driving the landing wheels when in retracted position. It will be understood however that this arrangement is shownfor purposes of illustrating my invention and that other sources of power may be used than electric motors. In certain instances it is desirable to transmit the driving force from some auxiliary motor in the plane in order to save the additional weight of two motors. On some diierently designed airplanes it is possible to hook up the same pivotally mounted angularly shiftable friction wheels to a near-by auxiliary motor by means of a suitable extension. A belt drive may also be employed from mechanism. driven from the main engine if desired by which the friction wheels which are moved into .contact with the landing wheels may be driven.

I have discovered that many of the heavier bombers develop trouble with what'is apparently weak landing gears. 'I'he stronger the landing gear the heavier it must be. In order to conserve weight, the landing gear on some planes is not too v strong. 'I'here have been many cases where heavy planes come in for a landing and the landing gear folds up under the load.

Each wheel on certain bombers weighs almost 600 pounds. In other words, the plane comes in with idle landing wheels that weigh over half a ton. The instant after they hit the ground, that half ton of dead Weight is spinning at 120 M. P. H. I believe this is the shock that cracks the landing gear. If the wheels were rolling along at the same speed at which the plane was landing, in accordance with my invention, there should be very little shock to the landing gear.

The giant cargo planes and super transports that are now being designed for production in the very near future may develop even further landing gear troubles because of their terrific weights.

My invention provides that safety factor necessary to avoid crack-up oi landing gears by eliminating the terrific strains involved in the landing of such heavy aircraft. Moreover, when such heavy craft makes an abrupt landing with half worn tires, the tires will sometimes blow and upset the plane. accidents. These could be avoided if the wheels were spinning prior to landing. Furthermore,

the use of my invention provides considerable saving in tires which is so essential under existing conditions in which the rubber shortage is so acute.

While I have described my invention in certain preferred embodiments, I desire that it be understood that modifications may be made and that no limitations upon my invention are intended other than may be imposed by the scope of the appended claims.

What I claim as new and desire to secure by Letters Patent of the United States is as follows:

There have been a number of such` 1. An aircraft landing system comprising in combination with the wing structure of an aircraft including landing gear having rotatable landing wheels retractible into and extensible out of said wing structure,l pivotally mounted angularly shiftable 'electrically driven motor devices disposed in said wing structure in positions adjacent the retracted position of the landing gear, friction wheels ,driven by said motor devices, means for angularly shifting said motor devices yfor eilecting engagement between said friction wheels and said landing wheels for rotatably driving said landing wheels at approximately landing speed while said landing gear is in retracted position within said wing structure.

2. An aircraft landing system comprising in combination with the wing structure of an aircraft including landing gear having rotatable landing wheels retractibl into and extensible out of said wing structure, pivotally mounted angularly shiftable electrically driven motor devices disposed in said wing structure in positions adja-l cent the retracted position of the landing gear, friction wheels driven by said motor devices, means for angularly shifting said motor devices for eiecting engagement between said friction wheels and the treads ois'aid landing wheels for driving'said landing wheels at landing speed while said landing gear is in retracted position within said wing structure prior toextension thereof from said wing structure.

3. An aircraft landing system comprising in combination with the wing structure of 'an aircraft including landing gear having rotatable landing Wheels retractible into and extensible out loi' said wing structure, pivotally mounted angularly shiftable electrically driven motor devices disposed in said wing structure in positions adj a.- cent the-retracted position of the landing gear, friction wheels driven by said motor devices, means for angularly shifting said motor devices for effecting engagement between said friction Wheels and the sides of said landing wheels for drivingv said landing wheelsat approximately landing speed while said landing gear is in retracted position within said wing structure prior to extension thereof from said wing structure.

4. Aircraft landing mechanism comprising extendable and retractible aircraft landing gear including rotatable landing wheels, separate driving motors mounted adjacent the retracted position of said landing gear, a friction driving wheell 5. Aircraft landing mechanism comprising ex' tendable and retractible aircraft landing gear including rotatable landing wheels, separate driving motors mounted adjacent the retracted position of said landing gear, a friction driving wheel individual to each of said driving motors and engageable with the respective landing Wheels for imparting rotary movement to said landing wheels while said landing gears are in retracted position, means individual to each of said driving motors for` manually starting said motors, indicators for representing the running condition of said motors, and automatic means Y larly shiftable electrically driven motor devicesv disposed in said wing structure` in positions adjacent the retracted position of the landing gear, friction wheels driven by said motor devices, means for angularly shifting said motor devices for eiecting engagement between said friction wheels and said landing wheels for rotatably driving said landing wheels at approximately landing speed while said landing gear is in retracted position within said wing structure, and

means for manually starting said motor devices and operating said aforesaid means for shifting said motor devices to positions on which the friction wheels engage said landing Wheels, and

separate means for automatically interrupting the operation of lsaid motor devices and restoring said motor devices to normal position when said landing wheels reach a predetermined speed of rotation.

'7. An aircraft landing system comprising in combination with the wing structure of an aircraft including landing gear having rotatable landing wheels retractible into and extensible out of said Wing structure, pivotally mounted angularly shiftable electrically driven motor devices disposed in said wing structure in positions adjacent the retracted position of the landing gear, friction wheels driven by said motor devices, means for angularly shifting said motor devices for effecting engagement between said friction wheels and said landing wheels for rotatably driving said landing wheels at' approximately landing speed while said landing gear is in retracted position within said wing structure, means for manually starting said motor devices and operating said aforesaid means for shifting said motor devices to positions on which the friction wheels engage said landing wheels, separate means for automatically interrupting the operation of said motor devices and restoring said motor devices to normal position when said landing wheels reach a predetermined speed of rotation, and visual indicator means associated with said first mentioned means for indicating the running or idle condition of said motor devices.

8. An aircraft landing system comprising in combination with the airfoilsof an aircraft, landing gear retractible into and extendable out of said airfoils, rotatable wheels carried by said landing gear, an electrically driven motor mounted within each airfoil adjacent the retracted position of said landing gear, a friction drive wheel driven by said motor and engageable with said wheel in the retracted position of said landing gear for driving the landing wheel at approximately landing speed prior to the extension of said landing gear to landing position, a. centrifugally operated switch connected with each of said friction drive wheels and disposed in series with the associated electrically driven motors for opening the motor circuits when said rotatable f wheels reach a predetermined speed of rotation.

9. An aircraft landing system comprising in combination with the wing structure of an aircraft including landing gear havlng rotatable landing wheels retractible into and extensible out of said wing structure, pivotally mounted angularly shiftable electrically driven motor devices disposed in said wing structure in positions adjacent the retracted position of the landing gear, friction wheels driven by said motor devices, means ior angularly shifting said motor devices for effecting engagement between said friction wheels and said landing wheels for rotatably driving said landing wheels at approximately landing speed whilesaid landing gear is ln retracted position within said wing structure, an electric control circuit including a power source, a series circuit through each motor device and including in series: a main switch, a holding magnet for said main switch connected in said series circuit, a centrifugally operated switch driven by said motor device, and a control solenoid for controlling the operation of said first mentioned means for angularly shifting each motor device for effecting engagement between the associated friction wheel and the associated landing wheel.

10. An aircraft landing system 'comprising in combination with the wing structure of an aircraft including landing gear having rotatable landing Wheels retractible into and extensible out of said wing structure, pivotally mounted angu- .Y larly shiftable electrically driven motor devices disposed in said wing structure in positions adjacent the retracted position of the landing gear, friction wheels driven by said motor devices, means for angularly shifting said motor devices for effecting engagement between said friction wheels and said landing wheels for rotatably driving said landing wheels at approximately klanding speed while said landing gear is in retracted position within said wing structure, an electric control circuit including a power source, a series circuit through each motor device and including in series: a main switch, a holding magnet for said main switch connected in said series circuit, a centrifugally operated switch driven by said motor device, a control solenoid for controlling the operation of said first mentioned means for angularly shifting each motor device for effecting engagement between the associated friction` wheel and the associated landingl wheel, and indicator means for visually indicating the running and idle condition of said motor devices.

11. An aircraft landing system comprising in combination with the wing structure of an aircraft including landing gear having rotatable landing wheels retractible into and extensible out of said wing structure, pivotally mounted angularly shiftable electrically driven motor devices disposed in said wing structure in positions adjacent the retracted position of the landing gear, friction wheels driven by said motor devices, means forangularly shifting said motor devices for effecting engagement between said friction wheels andsaid landing wheels for rotatably driving said landing wheels at approximately landing speed while said landing gear is in retracted position within said wing structure, an electric control clrcuit including a power source, a series circuit through each motor device and including in series: a main switch, a holding magnet for said main switch connected in said series circuit, a centrifugally operated switch driven by said motor device, a control solenoid for controlling the operation of said rst mentioned means for angularly shifting each motor device for effecting engagement between the associated friction wheel and the associated landing wheel, and spring means for restoring said motor devices to idling position with the friction wheels out of engagement with said landing wheels when said series circuit is interrupted.

12. Aircraft landing mechanism 4comprising extendable and retractible aircraft landing gear including rotatable landing wheels, separate 5 electrically driven motors mounted adjacent the retracted position of said landing gear, a friction driving wheel individual to each of said driving motors and engageable with the respective landing wheels for imparting rotary movement to 10 

